Constant current regulation



Nair. E5, 3932. NYQUIST 1,8875%) CONSTANT CURRENT REGULATION Filed Sept. 18, 1928 Vlt'aye INVENTOR 0 fi ATTORNEY Patented Nov. 15, 1932 UNITED STATES,

PATENT OFFICE HARRY NYQUIST, OF MILLIBURN, NEW JERSEY, ASSIGNOR T AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK CONSTANT CURRENT REGULATION Application filed September 18, 1928. Serial No. 306,680.

This invention discloses an arrangement for delivering a constant current to a circuit supplied from a fluctuating source of potential. The scheme is especially applicable to telephone repeater circuits where it is desirable to supply the vacuum tube filaments with an approximately constant direct. current from a source of potential which fluctuates within fairly narrow limits.

The constant current regulation is obtained by inserting in the circuit to be regulated, a ballast lamp shunted by a suitable resistance. 'Such an arrangement when properly designed, as explained below, will insure a constant current flow'in the circuit under fluctuating conditions of the supply potential.

The use of such an arrangement in the filament circuit of vacuum tube repeaters has for one of its objects an increase in the useful life of the tubes forsuch service. For repeater use, a vacuum tube reaches the end of its use- :ful life when under operating conditions its change in gain exceeds a specified amount. By operating conditions are meant the fluctuating current values to which the tubes in present practice are subjected, due to the fluctuating potential of the filament battery. By insurjn a constant filament current to the tubes-this fluctuation in gain is avoided and 3.9 the useful life of the tubes thus considerably extended.

Even with a constant filament current supply the tubes gradually age in use to the point at which they do not emit suflicient electrons with the normal current supply. At this point the only alternative to discarding the tubes is to increase the filament current to a greater value and thus restore the original emissivity.

As a second novel feature, this invention discloses means for increasing the filament current in individual tubes as the emission begins to decrease. In this manner the useful life of the tubes is still further prolonged.

The novel features are best understood by reference to the drawing of which Figure 1 discloses certain voltage-current characteristics which explain the constant current regu-' lation; while Fig. 2 discloses a circuit arthroughresistance 4, while the other end is rangement embodying both thenovel features discussed above.

Referring to Fig. 1, curve 2 shows a typi- T cal voltage-current characteristic for a ballast lamp consisting of a filament of iron wire immersed in hydrogen at low pressure. For the voltage range E to E it will be noted that the slope of the characteristic curve is negative, and that the current decreases almost linearly with an increase in voltage. This suggests shunting the lamp by a positlve or simple resistance the slope of the volt.- age-current curve of which is e ual in magnitude to that of said lamp. ith such an arrangement an increment of voltage across the shunt circuit in the range E E would cause an increment of current to flow through the shunt resistance which would exactly 0&- set the corresponding decrement of current flowing through the ballast lamp. As result, the total current taken by the elements in parallel remains constant and unaffected by the voltage change.

Curve 1, Fig. 1, shows the voltage-current curve forsuch a shunting resistance. The slope of this curve is equal in magnitude but -opposite in sign to that of curve 2 between the voltages E and E Adding the abscissae of curves 1 and 2 gives curve 3, which represents the total current taken by the parallel circuit, i. e., ballast lamp plus resistance, for any given value of voltage impressed across the same. It is'evident from curve 3, that the current taken by the parallel circuit remains constant for voltage fluctuationsin the region E to E Referring now to Fig. 2, a plurality of vacuum tubes 1 are connected in series. One end of the circuit is connected to ground connected through the current regulating circuit 7 and battery 3 to ground. Circuit 7 comprises ballast lamp 5 shunted by a suitable resistance 6, to insure the type of voltage current curve shown by curve 3 of Fig. 1. If the source of voltage 3 normally fluctuates only within the voltage limits E to E, a constant current supply to the filament circuit is insured, thus extending the useful life of the tubes. The resistance 4 II constant magnitude comprising in combiserves to adjust the filament current to its proper value within the voltage range E to E2.

To further extend the useful life of tubes 1, each filament at the beginning of service is shunted by a suitable resistance 2, and the ballasting combination 7 so adjusted that the filaments receive the proper current under this condition. When any tube is found to have aged in serviceto' the point where its emission is insufiicient, the corresponding resistance 2 shunting that particular filament is disconnected, thereby causing an increase of filament current sufiicient to restore the tube to a condition of satisfactory emissivity, and further prolonging its useful life.

The circuit of Fig. 2 is, of course, onl one illustration of the many uses to whic the ballasting combination 7 could be put in regulating current to a constant value.

It is not essential that a ballast lamp be used to obtain constant current regulation in the manner described The same ideas could beapplied to other devices having char acteristics such that over a certain range the September, 1928.

slope between said limits of voltage fluctua tion, and in shunt withpsaid resistor a resistance having a voltage-current characteristic of positive slope equal in magnitude to said negative'slope.

In testimony whereof, I have signed my name to this specification this 12th day of HARRY NYQUIST.

current decreased linearly with increased voltage.

What is claimed is: 1. Means for obtainin a current flow of nation, a ballast resistor havin a voltagecurrent characteristic of approximately constant negative slope between certain voltage limits, and in shunt with said resistor a fixed resistance having a voltage-current characteristic of positive slope equal in magnitude to said negative slope.

2. In an electrical circuit including a. source of potential subject to'fluctuation between certain limits, means for obtaining a flow of current of constant magnitude in said circuit, comprising in combination, a ballast lamp having a voltage-current characteristic of approximately constant negative slope between said limits of potential fluctuation, and in shunt with said lamp a resistance having a voltage-current characteristic of positive slope equal in magnitude to said nega tive slope.

' 3. In combination, a load circuit, a source of voltage subject to fluctuations connected in said circuit, and a first and a second resistor connected in series with said circuit and in arallel with each other, said first resistor aving a voltage-current characteristic of approximately linear negative slope between certain limits of said voltage fluctuation and said second resistor having a voltage-current characteristic of positive slope equal in magnitude to said negative slope.

4. Means for maintaining in acircuit supplied from a source of potential subject to uctuation, a current of constant magnitude between certain limits of fluctuation ofsaid lio 

